1. Field of the Invention
The present invention generally relates to an automatic transmission control apparatus equipped with a neutral control configured to prohibit transmission of a creep torque to a drive wheel when a prescribed condition is satisfied.
2. Background Information
In a vehicle having an automatic transmission with a torque converter, a prescribed amount of torque (called “creep torque”) is produced when an accelerator pedal depression amount is zero while a traveling range, e.g., Drive or Reverse, is selected. When a driver depresses a brake pedal in order to overcome the creep torque and stop the vehicle while a traveling range is selected, a neutral control is executed whereby a holding element is released and the automatic transmission is put into a neutral state in order to avoid imposing an unnecessary load on the engine.
A known method of determining when to execute and end the neutral control is use a brake switch signal. More specifically, the neutral control is started when a brake switch outputs an on-signal and ended when the brake switch outputs an off-signal.
Since the brake switch outputs the on-signal in response to even a slight amount of brake pedal depression, there are times when the neutral control is executed even though the driver does not intend to stop. A feasible way of avoiding this problem is to set the on and off threshold values of the brake switch to higher values. However, since the brake switch serves as the signal for turning the brake lamps on and off, increasing the threshold values makes the brake lamps illuminate less readily and poses a problem from a safety standpoint. In short, it is not possible to accurately detect the driver's brake depression amount (intention to stop) based on a signal from a brake switch.
In response to this issue, Japanese Laid-Open Patent Publication No. 5-87236 discloses a technology whereby the start timing and end timing of a neutral control is determined based on a brake fluid pressure of a brake pedal instead of a brake switch. In Japanese Laid-Open Patent Publication No. 5-87236, a driver's intent to stop is determined based on an operation amount (brake fluid pressure) of a brake pedal in connection with executing a creep prevention control and a neutral control. Additionally, in Japanese Laid-Open Patent Publication No. 5-87236, a different threshold value of the operation amount of the brake pedal is used for starting the neutral control than for ending the neutral control. More specifically, a threshold value A for the neutral control is set to a larger value than a threshold value B for ending the neutral control (threshold value A>threshold value B). As a result, various effects are achieved, e.g., the driving/operating performance is improved, the shock that occurs when the neutral control ends is reduced, and gear hunting is prevented from occurring when the neutral control is started and ended.
In view of the above, it will be apparent to those skilled in the art from this disclosure that there exists a need for an improved automatic transmission control apparatus. This invention addresses this need in the art as well as other needs, which will become apparent to those skilled in the art from this disclosure.